#1501 feat(sdk-swift): add fleet terminal sessions

Summary

• add AgentClient.terminals as the typed Swift SDK surface for hosted fleet terminal discovery and attach
• own ticket creation, same-origin WebSocket validation, bounded reconnect, ordered acknowledged input, resize, correlated snapshots, and structured close in the SDK
• report the broker delivery-mode revision on ready and use compare-and-set restoration so detach cannot overwrite a concurrent operator change
• extend the broker terminal lane with explicit snapshot correlation and delivery-state readiness

Chief and other native clients only provide an agent name, mode, renderer, and user input. They do not discover nodes, shell out, or implement Relaycast terminal frames.

Dependency

• hosted participant authorization and frame routing: AgentWorkforce/relaycast-cloud#59

Validation

• swift build --package-path packages/sdk-swift --target AgentRelaySDK
• full broker suite: 923 passed, 4 environment-gated ignored; continuity/wire/journal integration tests passed
• targeted terminal protocol and delivery-state tests passed
• cargo fmt --all -- --check
• git diff --check

Swift XCTest execution is unavailable under the active Command Line Tools-only installation (no such module XCTest); the SDK target itself builds cleanly.